In the early days of dry-cleaning, kerosene was used to remove oil based stains from fabric. This proved dangerous as kerosene is highly flammable. Around the time of World War II, the dry cleaning industry used other volatile synthetic solvents such as, carbon tetrachloride and trichloroethylene. During the late 1940's and early 1950's these toxic compounds were replaced with perchloroethylene (PERC), which became the solvent choice for the industry. PERC was thought to be safer than its predecessors and produced a cleaner product, in less time, and with less equipment. This allowed for dry cleaning establishments to open in retail venues and offer quick turn around times.
PERC is an excellent dry-cleaning solvent. However, it has since been discovered that PERC is carcinogenic and an environmental hazard. There are some municipalities which have banned the use of PERC in the dry cleaning industry. Alternative dry-cleaning solvents include Stoddard (hydrocarbon) solvents and siloxanes.
Whichever solvent is employed, professional dry-cleaning processes often use distillation to clean the solvent between uses. This process has a large energy cost and produces dangerous solvent vapors which must be recaptured and condensed for further use.
A frustrating issue faced by the dry-cleaning industry is the non-uniformity of dirt and stains which occur on article, particularly clothing. Stains can be separated into two general categories: lipophilic or oil-based compounds such as those left by body oils, fats and greases, cosmetics, and other highly aliphatic materials; and hydrophilic or water-soluble compounds such as fruit juice, ink and wine. A hydrophilic solvent will not dissolve oil-based stains and, conversely, a lipophilic solvent will not dissolve water-based stains.
Common practice in the dry cleaning industry is to pre treat or “spot clean” the water-based stains, and then dry-clean the garment, followed by a post treatment of any remaining water-based stain to ensure removal. This is a laborious process involving a close visual inspection of each garment, followed by the marking and treatment of stains with an appropriate cleaning method. To conduct the process in an acceptable manner not only requires considerable time and extra cleaning equipment, but also extensive experience to recognize and employ the correct cleaning techniques. Thus, it would be beneficial to use a solvent solution which could treat both water and oil-based stains, thereby eliminating the need for extra workers to inspect and treat garments with mixed stains.
There is no acceptable solution to the problem of mixed stains available to the individual consumer. Many garments are “dry-clean” only, as certain articles, such as silk and wool, will shrink or deform if they are washed in water. Therefore, these materials must be sent to a professional dry cleaner, which is an expensive and time-consuming endeavor. Furthermore, as discussed above, dry-cleaning may not be effective on all types of stains and workers may fail to detect all remaining stains before the article is returned to the consumer.
It would, therefore, be desirable to have a dry-cleaning cleaning fluid which is effective on both oil-based stains and water-based stains, and would not damage water-sensitive articles. It would be more desirable to have such a cleaning fluid that were also safe enough to be used by consumers in their home as well as by professional dry cleaners.
A further problem associated with the dual phase cleaning emulsions of the present invention is their propensity to form inverted emulsions which appear as a gel in the wash solution or on the articles in the washing machine. The use of common laundry detergents, particularly those utilizing surfactants of an anionic nature such as sodium dodecylbenzene sulfonate and sodium lauryl sulfate, when emulsified in siloxane fluids with relatively small amounts of water or other immiscible polar solvents, provided effective cleaning while preserving the benefits of dry cleaning. However, a difficulty observed with this technique arises from the porous nature of the fabric and the phase behavior of the emulsions. For example, in cases where the polar phase has been used in excess, typically when the polar solvent's saturation limit in the clothing has been exceeded, a potential arises for the inversion of the emulsion.
For example, an initial water-in-oil emulsion can be partially inverted to a thick, slippery gel comprising an oil-in-water emulsion in which the water phase is now the continuous phase. This gel is insoluble in the primary water-in-oil emulsion. Further, in a washing machine, the gel cannot be easily rinsed away. It clings to the articles giving a greasy feeling and irritating detergent residue may be left on the clothing upon drying. If the gel is removed by mechanical action, the viscous nature of the gel allows it to clog filters and screens and interfere with the proper operation of the machine.
The use of inorganic salts such as sodium chloride will suppress the formation of an inverted emulsion. This suppression occurred at levels of about 0.2M NaClaq; however, the cleaning ability of the detergent also declines with increasing salt content. Lowering the salt content improves cleaning, but then the risk of gel formation rises. Therefore, it would be beneficial to have a method of suppressing gel formation independent of cleaning performance.
A critical parameter to any detergent is its ability to self-assemble and form micellar structures. Intermolecular attractions between the surfactant molecules cause them to group together and structurally align. This same factor is important in bubble, foam, and film formation. A good film is elastic enough to withstand deformations because of the good intermolecular attraction between surfactant molecules. However, the bonding must not be so tight as to prevent the ready diffusion of the surfactant molecules to weak spots in the film. These properties are strongly governed by the degree and type of self-assembly.
An old-fashioned notion of a good detergent required soaps to lather and foam, and although this is not a true statement, testing suggests that detergency and foaming are physically related. Not surprisingly, emulsions are another area in which dynamic and equilibrium film properties play a considerable role. The outside of an emulsion droplet has a film that acts much like the bubbles described above.
In situations where foaming and emulsions are not desirable, additives are employed. Some act by altering the packing ability of the surfactant. Previously flexible films can be made brittle with additional bonding (typically achieved with advantageous calcium ions in water washing) or weakened by the creation of flaws in the film. Addition of the bulky tributylphosphate bromide is one well-known reagent for the latter purpose.
The gel, an oil-in-water emulsion, occurring in the wash emulsion has been observed to be exceeding stable with lifetimes of over one year. Stable emulsions usually have surfactants capable of forming good films. From the above discussion, one way to prevent an emulsion's formation would be to change the film properties of the detergent's surfactant.
It would, therefore, be desirable to find an additive which would interact with the emulsified cleaning solution to effect the film properties of the detergent's surfactant to prevent gel formation, yet not interfere with the overall cleaning properties of the wash liquor.
Sometimes the cleaning ability of the wash emulsion is not enough to completely remove certain stains. The incorporation of a pre-spotter or pre-treatment step before the wash will often provide the additional cleaning power necessary to remove these stains. The infinite combinations of stains and soils, fabrics, dyes, weaves and yarns, and the physical condition and amount of each stain (such as degree of oxidation and set) make the task of developing a general detergent capable of removing every stain a very daunting chemical task. Realistically, most consumers accept that large stains, stains that have completely saturated the fabric, old stains, and unusual stains such as paint and tar, are unlikely to be removed by household detergents in water washing, and if these stains are to be removed, special treatments and detergents are required. Although the treatments may work by various actions, such as bleaching, enzymes, concentrated surfactants, pH gradients, emulsifiers and solvents, the pre-spotters share the characteristic of being applied directly to the stain, and only on the stain, and is applied by hand prior to the machine wash.
One problem associated with using household pre-spotters, particularly water based pre-spotters with siloxane-only water-free washing is the increased potential to make the stains worse, and possibly create new stains caused by residual detergents. It would, therefore, be desirable to employ a pre-spotter that is compatible with a siloxane based cleaning emulsion.